A traditional conducting wire of a light string unit for illumination and decoration composes of a conductor and a PVC shell. For this reason, the traditional conducting wire of the light string unit can not reaches a requirement on tensile strength of a conducting wire in the UL 588 criterion. Therefore, in one of existing improvements, one half length of the conducting wire of the light string unit comes into series connection with a lamp body, and the other half length of the conducting wire is folded back to twist the half conducting wire of the light string unit (which is so called as twisted wire). This kind of improvement has following disadvantages: materials are wasted since only half length of the conducting wire comes into series connection with the lamp body; conducting wires between each two lamp bodies are necessarily manually twisted after the light string is processed, which consumes a great of working hours and can not guarantee the quality of twisted wires; in addition, since the conducting wires are electrically connected in whole length, if the PVC shell is cracked in the twisting process, two conductors of twisted wires may easily come into contact to further cause a short circuit to damage the light string unit when the light string unit is energized.
In order to eliminate the disadvantages of the above improvement, in another one of improvements, a non-conducting wire (which is so called as fake wire) is additionally provided between each two lamp bodies of the light string unit, wherein a connection part for the non-conducting wire is provided on a bottom of the lamp body, both ends of the non-conducting wire are fixedly connected to the connection part on the bottom of the lamp body respectively, or are folded to be embedded in the connection part on the bottom of the lamp body, and finally the conducting wire and the non-conducting wire are twisted together. In this kind of improvement, however, materials of the non-conducting wire are also consumed, and the connection part for the non-conducting wire is necessarily provided on the bottom of the lamp body so as to make the lamp body or the structure of the light string become relatively complex; working hours are necessarily increased to install the non-conducting wires; especially, if the non-conducting wire and the connection part on the bottom of the lamp body are unreliably connected such that they could be released in a pulling process, the light string unit would have only the traditional conducting wire connection, the tensile strength of which can not reach the requirement of the UL 588.